We are synthesizing a variety of new organoboron compounds to be tested as possible antileukemia agents and also as possible agents for the boron-10 neutron capture therapy of brain tumors. Most of the current investigation is based on the chemistry of methanetetraboronic esters, C(B(OR)2)4, and related compounds, which can be used to introduce boron into a wide variety of structures having functional groups likely to be active in biological systems. Emphasis has been placed on pyrimidine and amino acid derivatives. We also have some interest in carboranyl-substituted pyrimidines and carborane anions.